The present invention relates generally to touch control arrangements for apparatus incorporating a plurality of operating components arranged for selective actuation in accordance with user generated input data. More specifically, this invention relates to touch control arrangements incorporating tactile or capacitive touch keyboard panels for use with domestic appliances such as ranges and microwave ovens.
Touch control arrangements are commonly used for user data entry for appliance controls. Such arrangements typically include touch panels of the tactile or membrane switch type or of the capacitive touch type. In the tactile or membrane switch touch panel, each key of the input keyboard is actuated by pressure applied to the key by the user which closes electrical contacts. In the capacitive touch panel, the keyboard is an array of touch pads, each forming a plate of a sensor capacitor and the keys are actuated by the touch of a human finger. When a pad is touched, the body capacitance of the user changes the effective capacitance associated with the touch pad. This change in capacitance attenuates the control signal from the touch panel, thereby indicating to the electronic control device which pad has been actuated.
Generally, both the tactile touch and the capacitive touch panels employ keyboard arrays in which the keys or pads are arranged in row and column matrices. The keyboard array has a separate input line associated with each column and a separate output line associated with each row of keys or touch pads. The electronic controller, typically a microprocessor, monitors the keyboard array for inputs by periodically applying a control or strobe pulse sequentially to each of the column input lines and monitors each of the row associated output lines. Thus, in effect, each individual switch key or touch pad is periodically polled by the microprocessor which identifies the actuated key by sensing a change in the magnitude of the strobe signal.
While this matrix type array performs satisfactorily, it has several drawbacks including: the number of input and output lines needed to couple the touch panel to the controller and the associated connections for these lines adds significantly to the expense of the keyboard array; the length of the connecting lines must be limited to minimize the capacitive effects between the lines; the control signal applied to the keyboard comprises a relatively high frequency pulse train presenting electro-magnetic interference problems; and the interfacing with the microprocessor ties up several microprocessor input and output ports which could be advantageously employed for other purposes.
It is therefore an object of the present invention to provide a touch control arrangement which overcomes the above mentioned drawbacks of prior art arrangements by employing oscillating means responsive to the user actuable touch keys, which operates to generate a control signal at a plurality of frequencies, the frequency being determined by the selective touching of the touch keys by the user, and an electronic controller which responds to the frequency of the control signal.
It is a further object of the present invention to provide a touch control arrangement of the aforementioned type which employs only two lines for interfacing with the electronic controller, thereby permitting relatively long connections, freeing up a number of controller input and output ports and significantly reducing the cost of the touch control arrangement.
It is a further object of the present invention to provide a touch control arrangement of the aforementioned type which employs a relatively low frequency sinusoidal signal, thereby eliminating electromagnetic interference problems.
It is a further object of the present invention to provide a control arrangement of the aforementioned type which is applicable to both tactile touch and capacitive touch type keyboard structures.